Diet, Glycogen Reserves and Resistance to Fatigue in Hatchery Rainbow Trout

Abstract

In a stream occupied by a resident wild trout population, mortality of introduced hatchery trout is greater than when similar trout are released in a barren stream. From this it has been inferred that in the occupied stream the new-comers cannot find niches and succumb to exhaustion in the open current. A conspicuous rise in blood lactic acid in planted hatchery trout supports this inference.In the present experiment rainbow trout of identical brood stock were raised on two diets; one group received a complete dry pelleted ration, the other, ground liver. After 35 weeks the trout were subjected to varying degrees of exercise, following which blood lactate and liver and muscle glycogen were assayed. It was found that the pellet-fed trout had more glycogen stores before exercise; that during exercise this group maintained its liver glycogen but lost about half the muscle glycogen after 15 minutes of exercise. After 12 hours' rest muscle glycogen had risen to the normal level. In the liver-fed trout liver glycogen was depleted to one-half after 15 minutes' exercise and muscle glycogen fell to one-fifth or lower. Twelve hours rest failed to restore either liver or muscle glycogen. Prolonged exercise in a current of one mile per hour reduced glycogen to about 1/4 in the liver-fed fish; some died during the test, and none returned to normal metabolic states after 24 hours. It is concluded that exhaustion of metabolites such as glycogen plays some part in deaths of planted trout, and that the hatchery diet can materially affect the ability of the fish to survive.